Researchers developed a technology that can shape the spectrum of light emitted from a laser frequency comb across the visible and near-infrared wavelengths with more precision than previously possible. This research could provide an important tool in the hunt for exoplanets, Earth-like planets outside our solar system. When searching for exoplanets, astronomers use high-precision spectroscopy to detect tiny shifts in starlight that reveal a star’s subtle wobble due to an orbiting planet. But for Earth-sized planets, these wavelength changes are smaller than the spectrograph’s natural instabilities, so laser frequency combs are needed to provide a reference. “Our spectral shaper can make the lines on a laser frequency comb more uniform, which allows the spectrograph to detect smaller stellar motions, such as those from Earth-like planets, that would otherwise be hidden in the noise,” said research team lead Derryck Reid. Researchers developed a new type of spectral shaper that can shape the spectrum of 10,000 lines of light from a laser frequency comb. The image shows the spatial light modulator they used with a 2D spectrum on the surface. Courtesy of Optica. The researchers’ spectral shaping method with a lab-based astronomical spectrograph can precisely control 10,000 individual lines of light, a roughly 10-fold improvement in performance over previous approaches. According to the researchers, this method could be used in fields such as telecommunications, quantum optics, and advanced radar, where precise control over the shape of light across broad bandwidths can improve signal fidelity, enable faster data transfer, and enhance the manipulation of quantum states. The researchers programmed various photos as target shapes on the two-dimensional spectrograph. Shown here is a team member’s dog (left) represented by thousands of laser frequency comb lines (right). Courtesy of Optica. Spectral shapers are used to fine-tune light to produce precisely defined spectral characteristics. This type of spectral shaping might, for example, be accomplished using a prism, which splits white light into various wavelengths along a line, forming a single spectrum. However, this one-dimensional line spectrum is not well matched to the two-dimensional grid of pixels in a spatial light modulator. Spatial light modulators enable programmable, pixel-by-pixel control of the light’s intensity and phase across the spectrum, enabling high-resolution shaping of complex sources such as laser frequency combs, where each mode can be adjusted independently. “For our spectral shaper, we took inspiration from the astronomical spectrographs on large telescopes, which split up the spectrum of light into many rows, a format that makes more efficient use of high-resolution two-dimensional camera sensors,” said Reid. “By substituting a spatial light modulator for the camera typically used in spectrographs, we could control the spectrum of light across a wide bandwidth much more precisely than ever before.” This research was published in Optica (www.doi.org/10.1364/OPTICA.571303).
